1. Field of the Invention
The present invention relates to an aluminum negative electrode battery comprising at least one of aluminum and aluminum alloy as a negative electrode active material.
2. Description of the Related Art
At present, manganese batteries and alkaline batteries are used widely in portable appliances. Manganese batteries and alkaline batteries comprise negative electrodes made of zinc and positive electrodes made of manganese dioxide, and have an electromotive force of 1.5 V. As portable appliances are advanced recently, primary batteries and secondary batteries having high voltage, large capacity and light weight are being demanded.
So far, various battery systems have been proposed, and it has been attempted to develop batteries of higher voltage, larger capacity, and lighter weight, but most of batteries are not developed as commercial products owing to lack of reliability.
Most important problems relating to reliability are liquid leak and heat generation.
For example, the primary battery using aluminum as negative electrode is expected to have higher voltage, larger capacity, and lighter weight as compared with the primary battery using zinc as negative electrode, and has been well researched. For example, U.S. Pat. No. 2,838,591 discloses a battery comprising a positive electrode made of manganese dioxide, a negative electrode made of aluminum, and an electrolyte made of weak acidic aqueous solution of aluminum chloride. This battery, however, has a problem in reactivity between the aluminum used as the negative electrode and the electrolyte, and is hence large in self-discharge, large in generation of hydrogen gas, and small in capacity.
More recently, a highly practical aluminum negative electrode battery has been proposed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 2001-319662. In this aluminum negative electrode battery, however, even if there is no factor inducing generation of hydrogen gas such as external short-circuit or abnormal high temperature, the negative electrode and electrolyte react with each other usually to generate a large volume of hydrogen gas, and a large discharge capacity cannot be obtained. Aside from generation of a large amount of gas during discharge, leaks may occur due to the osmotic pressure phenomenon, due to dissolution of discharge products of the negative electrode into the electrolyte, thus it is far from commercial production.
On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 8-77996 proposes preventing leakage or scattering of an electrolyte of the battery, while releasing the gas in the battery to the exterior, by arranging a water repellent polymer film having gas permeability but preventing permeation of liquid between the gasket and the negative electrode bottom plate.
However, a large discharge capacity could not be obtained in the battery disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-77996.
On the other hand, claim 1 in Jpn. Pat. Appln. KOKAI Publication No. 2000-113871 discloses an alkaline secondary battery having a separator formed from a nonwoven fabric of hydrophilic polyolefin synthetic resin fiber with a contact angle to pure water of 0° to 100°. The definition of the contact angle is defined in paragraph [0015]. That is, a nonwoven fabric of about 2.5×10 cm is placed horizontally, about 10 μL of pure water is dropped on the nonwoven fabric, the fabric is left for 1 minute, and pure water is absorbed in pores of the nonwoven fabric. The contact angle of water drops on the nonwoven fabric surface is measured by an optical microscope such as goniometer type contact angle measuring instrument, and the obtained measurement is the contact angle to pure water. As described in this paragraph [0015], “the nonwoven fabric has an excellent hydrophilic property when the contact angle is small, which means that the nonwoven fabric itself is excellent in the holding performance of electrolyte, and when this value is larger, to the contrary, the nonwoven fabric shows a water repellent property, which means that the holding performance of electrolyte is poor. The contact angle of the nonwoven fabric of polyolefin synthetic resin fiber without hydrophilic treatment is about 120 to 130°.”